1. Field of the Invention
This invention relates to a slave petal for the divergent section of a variable geometry convergent-divergent exhaust nozzle for gas turbine propulsion units, used as the means of propulsion in aviation.
More specifically, the exhaust nozzle to which this invention refers is of the axisymmetric type, including a convergent section followed, in the direction of the flow, by a divergent section, both formed of master petals connected to each other by linkages, and slave petals also connected together by linkages. The convergent section defines a throat of variable area and the divergent section, also with variable geometry, can be actuated in order to vector the gas flow, and therefore the thrust, in any direction on a cone located around the longitudinal axis of the propulsion unit.
2. Description of Related Art
The maneuverability of aircraft is an essential factor. This maneuverability which to date has been achieved by aerodynamic forces, can be substantially improved by modifying the vectoring of the flow starting from its normal axial direction of action.
Vectoring of the gas flow has been done for many years in rocket engines. There, the systems are much simpler since the exhaust nozzles have constant geometry.
Variable geometry convergent-divergent exhaust nozzles are a relatively recent introduction in supersonic aircraft powered by turboreactor or turbofan engines.
In this class of exhaust nozzle, the vectoring of the flow is still not in an operational state but is only at the research or development phase. Those that are at a more advanced state are the bidimensional type, in which the flow is vectored solely in one plane.
Carrying out vectoring of the flow in exhaust nozzles with axial symmetry has a special advantage since the direction of the flow can then be varied in any axial plane, the pitch and yaw planes being particularly important.
Several patents exist on mechanisms for vectoring of the flow in this class of exhaust nozzle, since it is theoretically possible to carry this out in various ways, though it is very difficult to ensure that there are no major complications.
Vectoring only the divergent section of the exhaust nozzle, downstream of the throat area, has the advantage that the perturbations induced by the vectoring are not transmitted upstream of the propulsion unit and the sealing of the interstices on the different moving parts is simplified. Even so, the problem of the sealing between divergent master petals during vectoring of the flow remains. In this regard, U.S. Pat. No. 4,994,665 or Spanish Patent Application No. 9200369 teach different designs of exhaust nozzle in which only the divergent section, or part of it, respectively, is vectored.
With the aim of solving the sealing of the interstices between divergent master petals, there exists various solutions such as those described in U.S. Pat. Nos. 4,690,330; 4,662,566; 5,039,014; 5,076,496 and Spanish Patent Application No. 9200369.
The present invention describes and claims a divergent slave petal for sealing longitudinal interstices between contiguous divergent master petals, in addition to pointing out special advantages offered in comparison with other systems that have been the subject of previous patents.
The geometry of the longitudinal interstices between divergent master petals changes during vectoring of the flow, going from an approximately rectangular shape to that of a ruled surface whose sides cease to be parallel.
In U.S. Pat. Nos. 4,690,330 and 4,662,566, a divergent slave petal is formed from a plurality of overlapping segments welded together and to a longitudinal dorsal metal sheet in specific areas, in such a way that the effect of the temperature gradient between the surface in contact with the gases and the external surface of the slave petal is absorbed by allowing a certain relative movement between the segments.
In order to seal the longitudinal interstice between divergent master petals during vectoring of the flow, U.S. Pat. No. 5,039,014 describes another solution that consists of a dorsal bar on which is mounted a plurality of segments that can rotate around that bar. Although this solution solves the problem of sealing the interstice, the assembly of segments creates a wall of considerable roughness and with a multitude of ridges transverse to the direction of the flow.
U.S. Pat. No. 5,076,469 describes a divergent slave petal formed from a metal sealing sheet linked to a continuous support element in such a way that allows a certain relative movement between both in order to allow thermal differential movements.
Spanish Patent Application No. 9200369 claims an asymmetrical variable geometry vectoring exhaust nozzle for gas turbine propulsion units.
That exhaust nozzle includes a divergent section and a convergent section, both formed from master petals and slave petals, and which includes governing and external radial supports for regulating the throat area and a regulator for regulating the vectoring of the flow, characterized by the fact that the variation in the throat area and the vectoring of the flow is carried out by a single governing system.
This single governing system is made up of three annular pieces, concentric with each other and with the axis of the propulsion unit, and of a plurality of linear actuators linked by the upstream end to the structure of the propulsion unit.
These annular pieces are connected together and to the structure of the propulsion unit by linkage elements and guide devices, which allow the joint axial displacement of the three annular pieces by an equal amount with respect to the structure of the propulsion unit, as well as a relative rotary movement of the intermediate and external annular pieces between themselves and with respect to the internal annular piece in any direction, thereby allowing the external annular piece to be inclined in any direction, with the center of rotation in the axis of the propulsion unit.
The convergent master petals are each connected at the upstream end to the internal annular piece by tangential cylindrical linkages with an axis disposed perpendicular to the axis of the propulsion unit. The external annular piece is in turn connected by spherical linkages to the downstream end of the linear actuators mentioned above.
The mechanism for varying the throat area A8 includes a rod connected at one end, via a linkage, to the convergent master petal, while the other end is connected via another linkage to the fixed structure of the exhaust nozzle housing.
The master petals in the divergent section are transversely subdivided into two segments joined together by a cylindrical linkage with an axis disposed perpendicular to that of the linkage between master petals in the convergent and divergent sections, the downstream segment being joined to the external annular piece by a strut, which is connected to this segment via a spherical linkage and to the external annular piece via a tangential cylindrical linkage with an axis disposed perpendicular to that of the propulsion unit.
The upstream segment of the divergent master petal is connected at its upstream end to the corresponding convergent master petal via a tangential cylindrical linkage with an axis disposed perpendicular to the axis of the propulsion unit.
The external annular piece includes two half-ring segments interconnected with linkages and supported by four linear actuators.
This design, including two half-rings moved by four linear actuators, allows the outlet area A9 to be varied for a fixed value of the throat area A8.
In Spanish Patent Application No. 9200369 discussed above, the problem of sealing the interstice existing between contiguous divergent master petals is solved by providing slave petals which include a foldable plate provided with hinged linkages in each of it folds, the freedom of rotation of the linkage being limited but sufficient so that the different components of that plate can adapt themselves to the configuration of maximum distortion of the geometry of that interstice.